The SRIH analog
octreotide is a potent GH-inhibiting agent that has been used to effectively treat patients with
acromegaly. To investigate the morphological changes induced by
octreotide on GH-producing
pituitary tumors, we examined 86
adenomas from acromegalic patients who participated in a multicenter study. GH- producing
pituitary adenomas removed from 43 patients treated preoperatively with
octreotide for 4 months were compared to those obtained from 43 untreated acromegalic patients. Tissue samples were studied by histology, immunohistochemistry, and transmission electron microscopy as well as light microscopic and ultrastructural morphometry. The morphological appearance of some
tumors was unaltered by
octreotide treatment. Necrotic changes were not apparent in any. Acidophilia and GH immunoreactivity were more pronounced in the
octreotide-treated
tumors. Perivascular and interstitial
fibrosis was more prevalent in the
octreotide group (72% vs. 42%). An increase in
hormone granularity was obvious in 4 of 15 densely granulated and 2 of 9 sparsely granulated (SG)
tumors from treated patients. A decrease in cell size was conspicuous in 4 of 15 densely granulated and 2 of 10 SG
adenomas. There was a slight downward trend in the cell and cytoplasmic size in all treated
tumors and a slight upward trend in secretory granule size in treated SG
adenomas. Only 2 of 9 SG
adenomas in the
octreotide group, however, demonstrated a statistically significant reduction in cell and cytoplasmic size. There was no statistically significant change in the size of nuclei, secretory granules, or lysosomes between the 2 groups. Decreased cell size and increased granularity were not linked, however. We conclude that there are no striking morphological alterations in GH
pituitary adenomas that can be consistently associated with
octreotide treatment.